Distance/velocity measuring method and radar signal processing device

ABSTRACT

A distance and speed measuring method and a radar signal processing apparatus using the method are provided which are capable of obtaining highly reliable measurement results while reducing the number of false targets and undetectable targets, by obtaining the relative distance and the relative speed of each target based on the frequencies of a beat signal of up (or down) phase alone through the use of information in a time series direction of the frequencies of the beat signal of up (or down) phase.

TECHNICAL FIELD

[0001] The present invention relates to a signal processing apparatusfor a radar installed on a movable object such as, for instance, avehicle, etc., and more particularly, to a distance and speed measuringmethod for detecting an object in the form of a target, and measuringthe relative distance and relative speed of the object, as well as to aradar signal processing apparatus using such a method.

BACKGROUND ART

[0002] In radars installed on vehicles, etc., the distance of a targetwhich is able to be measured thereby is generally in the range of aboutseveral m to about 200 m. As a radar system for detecting objects to bemeasured lying in such a range, there has often been used a well-knownFMCW (Frequency Modulated Continuous Wave) method which is described forexample in a book entitled “Introduction to Radar Systems” by M. I.SKOLNIK, McGRAW-HILL BOOK COMPANY, INC., (1962), a book entitled “RADARHANDBOOK” by M. I. SKOLNIK, McGRAW-HILL BOOK COMPANY, INC., (1970), abook entitled “Radar Technologies” compiled under the supervision ofTakashi Yoshida and edited by the Japanese Electronic InformationCommunications Society (1989), etc.

[0003]FIG. 3 shows the frequency characteristics of respective signalsrelative to time in an FMCW radar, in which a signal vs. time relationis illustrated in the case where the relative distance and the relativespeed of a target are obtained from a beat signal comprising atransmission signal of a continuous wave, which is frequency modulatedby a triangular wave and transmitted to the target, and a receptionsignal reflected from the target. Here, a modulation zone in which thefrequency of a carrier wave increases linearly with time is referred toas an up phase (a modulation frequency increase period). On the otherhand, a modulation zone in which the carrier frequency decreaseslinearly with time is referred to as a down phase (a modulationfrequency decrease period).

[0004] In FIG. 3, 1 designates a transmission signal, 2 a receptionsignal, and 3 a beat signal. Assuming that a frequency sweep width is B;a frequency sweep time is T; the speed of light is c: a wavelength is λ;the relative distance to a target is r; and the relative speed of thetarget is v, the frequency U of the beat signal 3 in the up phase andthe frequency D of the beat signal in the down phase are represented bythe following expression: $\begin{matrix}{U = {{{- \frac{2B}{cT}}r} + {\frac{2}{\lambda}v}}} & (1) \\{D = {{\frac{2B}{cT}r} + {\frac{2}{\lambda}v}}} & (2)\end{matrix}$

[0005] From these relations, the relative distance r and the relativespeed v of the target are obtained from the following expressions (5),(6) by using the results according to the subtraction and addition ofthe beat frequencies U and D, as shown by the following expressions (3),(4). $\begin{matrix}{{D - U} = {\frac{4B}{cT}r}} & (3) \\{{U + D} = {\frac{4}{\lambda}v}} & (4) \\{r = {\frac{cT}{4B}\left( {D - U} \right)}} & (5) \\{v = {\frac{\lambda}{4}\left( {U + D} \right)}} & (6)\end{matrix}$

[0006] Moreover, when there are a plurality of (N) targets, thefrequency Ui{i=Nu, Nu≦N} of the beat signal in the up phase and thefrequency Dj{j=Nd, Nd≦N} of the beat signal in the down phase areobtained. Therefore, a frequency pair (Ux, Dy) is selected based on acriterion set beforehand. The relative distance and the relative speedof each target are obtained by substituting the frequency pair for theexpressions (5) and (6).

[0007] For such a selection criterion, for example, peak intensities inthe frequency spectrum of the beat signal may be employed. In JapanesePatent Application Laid-Open No. 5-142337, pairs are determined in orderof the magnitude of intensity thereof. In addition, in Japanese PatentApplication Laid-Open No. 11-337635, there are used intensity patternswhich are obtained in a plurality of directions by scanning a beam.

[0008] These relative distance and relative speed of a target aregenerally measured repeatedly at preset time intervals.

[0009] However, in actuality, there arises a problem that the frequencyof the beat signal measured in a time series manner is varied accordingto the state of reflection from a target in the form of a vehicle, thecharacteristics of the components of a transmit and receive device,etc., thus resulting in unstable measurements of the distance and speedof the vehicle.

[0010] As solutions for such a problem, Japanese Patent ApplicationLaid-Open No. 5-142338, Japanese Patent Application Laid-Open No.5-150035, Japanese Patent Application Laid-Open No. 5-249233, etc.,disclose the use of information in a time series direction with respectto the frequency of the beat signal.

[0011] For instance, FIG. 4 shows the configuration of a signalprocessing part of a millimeter wave radar system disclosed in JapanesePatent Application Laid-Open No. 5-249233. The signal processing part 10illustrated is provided with an A/D (Analog to Digital) conversion part11, a frequency analysis part 12, a switching part 13, comparison parts14, 18, reference value forming parts 15, 19, storage parts 16, 20,variation removing parts 17, 21, and a distance and speed deriving part22.

[0012] Next, the operation will be described below. In the signalprocessing part 10 shown in FIG. 4, a beat signal 3 for a target isinput as an analog signal, and this beat signal is converted into adigital signal by the A/D conversion part 11. In the frequency analysispart 12, frequency analysis is performed through the use of an FFT (FastFourier Transform), etc., and the frequency U of the beat signal in anup phase and the frequency D of the beat signal in a down phase areextracted.

[0013] These frequencies are associated through the switching part 13with the point in time t at which they are measured. The frequency U isstored as U(t) in the storage part 16, and the frequency D is alsostored as D(t) in the storage part 20.

[0014] At time point t, the reference value forming part 15 sets areference value Uref(t) by using the past data stored in the storagepart 16. For instance, the reference value Uref(t) is set according tothe following expression (7) while assuming that an measurement intervalis Δt. $\begin{matrix}{{{Uref}(t)} = \frac{{U\left( {t - {\Delta \quad t}} \right)} + {U\left( {t - {{2 \cdot \Delta}\quad t}} \right)} + \cdots + {U\left( {t - {{5 \cdot \Delta}\quad t}} \right)}}{5}} & (7)\end{matrix}$

[0015] Similarly, the reference value forming part 19 sets a referencevalue Dref(t) by using the past data stored in the storage part 20. Forinstance, the reference value Dref(t) is set according to the followingexpression (8). $\begin{matrix}{{{Dref}(t)} = \frac{{D\left( {t - {\Delta \quad t}} \right)} + {D\left( {t - {{2 \cdot \Delta}\quad t}} \right)} + \cdots + {D\left( {t - {{5 \cdot \Delta}\quad t}} \right)}}{5}} & (8)\end{matrix}$

[0016] The comparison part 14 compares the frequency U(t) of the beatsignal in the up phase input thereto via the switching part 13 with thereference value Uref(t) set by the reference value forming part 15, anddetermines whether the frequency U(t) of the beat signal in the up phaseis data without any variation. For instance, whether the relationship ofthe following expression (9) is satisfied for a preset allowance orallowable width Wu is used as a criterion for such a determination.

|U(t)−Uref(t)|≦Wu   (9)

[0017] Similarly, the comparison part 18 compares the frequency D(t) ofthe beat signal in the down phase input thereto via the switching part13 with the reference value Dref(t) set by the reference value formingpart 19, and determines whether the frequency D(t) of the beat signal inthe down phase is data without any variation. For instance, whether therelationship of the following expression (10) is satisfied for a presetallowance or allowable width Wd.

|D(t)−Dref(t)≦Wd   (10)

[0018] The frequency U(t) of the beat signal in the up phase, for whichthe presence or absence of a variation was determined by the comparisonpart 14, is removed by the variation removing part 17 if determined asincluding a variation, whereas it is stored in the storage part 16 andinput to the distance and speed deriving part 22 if determined asincluding no variation.

[0019] Similarly, the frequency D(t) of the beat signal in the downphase, for which the presence or absence of a variation was determinedby the comparison part 18, is removed by the variation removing part 21if determined as including a variation, whereas it is stored in thestorage part 20 and input to the distance and speed deriving part 22 ifdetermined as including no variation.

[0020] Here, note that the frequency data U(t−Δt) and D(t−Δt) of thelast beat signal may be used instead of the frequencies U(t) and D(t) ofthe current beat signal when the frequencies of the beat signal havingbeen determined as including a variation are removed by the variationremoving part.

[0021] The distance and speed deriving part 22 calculates the distanceand the speed for the frequencies U(t) and D(t) of the input beat signalaccording to the expressions (5), (6).

[0022] The signal processing part of the known radar system isconstructed as mentioned above, and is able to suppress variations inthe beat frequencies in the time series direction. However, the priorart techniques including the above examples require a frequency pair ofbeat frequencies, i.e., a beat frequency in the up phase and a beatfrequency in the down phase, in order to obtain the distance and thespeed of a target.

[0023] Therefore, if one of the frequencies is not obtained, there willbe a (non-detection) target undetected due to the fact that no frequencypair is selected even though the target actually exists. On the otherhand, an incorrect or wrong frequency pair might be selected by the useof past beat frequencies instead of current beat frequencies notobtained, so that there will appear a target (false target) which cannot actually exist. As a result, the reliability of the measurementresults is deteriorated by these factors.

[0024] The present invention is intended to obviate the above-mentionedproblems, and has for its object to provide a distance and speedmeasuring method and a radar signal processing apparatus using themethod, which can obtain reliable measurement results while reducingfalse targets and undetectable targets by finding the distance and speedof a target based solely on the frequency of a beat signal of up (ordown) phase by using information in a time series direction of thefrequency of the beat signal of up (or down) phase.

SUMMARY OF INVENTION

[0025] In order to achieve the above object, a distance and speedmeasuring method according to the present invention, in which a relativedistance and a relative speed of a target are measured based on a beatsignal generated from a transmission signal and a reception signal of acontinuous wave radar, which is frequency modulated by a triangularwave, is characterized by including: a present measurement stage inwhich beat frequencies are extracted from the beat signal in an up phase(modulation frequency increase period) and in a down phase (modulationfrequency decrease period), and a frequency pair of beat frequenciescorresponding to the target is selected among the extracted frequencies,the relative distance and the relative speed of the target beingobtained based on the thus selected frequency pair as observed values,from which a relative distance, a relative speed and a beat frequency ofthe target are obtained as predicted values at the next observationtime; and next and following measurement stages in which relativedistances and relative speeds of the target at the next and followingobservation times are measured by using only beat frequencies in eitherone of the up phase and the down phase.

[0026] In addition, the next and following measurement stages ischaracterized in that priority is given to processing by beatfrequencies in either one of the up phase and the down phase, andprocessing by beat frequencies in the other phase alone is carried outonly when no target is detected in the one phase.

[0027] Moreover, the next and following measurement stages ischaracterized in that the observed values, the predicted values, andsmoothed values which are obtained from the observed values and thepredicted values are used when relative distances and relative speeds ofthe target at the next and following observation times are obtained byusing only beat frequencies in either one of the up phase and the downphase.

[0028] Further, the next and following measurement stages ischaracterized in that assuming that an predicted distance value, anpredicted speed value, an predicted beat frequency value in the upphase, an predicted beat frequency value in the down phase, an observedbeat frequency value in the up phase, and an observed beat frequencyvalue in the down phase, at the next observation point in time t+Δt, areRp(t+Δt), Vp(t+Δt), Up(t+Δt)x, Dp(t+Δt)x, U(t+Δt)x, and D(t+Δt)x,respectively, a smoothed distance value Rs(t+Δt) and a smoothed speedvalue Vs(t+Δt) are calculated by using the following expression:

Rs(t+Δt)=Rp(t+Δt)+α×{Up(t+Δt)x−U(t+Δt)x}

Vs(t+Δt)=Vp(t+Δt)+β×{Up(t+Δt)x−U(t+Δt)x}

Rs(t+Δt)−Rp(t+Δt)+α×{Dp(t+Δt)x−D(t+Δt)x}

Vs(t+Δt)=Vp(t+Δt)+β×{Dp(t+Δt)x−D(t+Δt)x}

[0029] where α and β are constants.

[0030] Furthermore, a radar signal processing apparatus according to thepresent invention, in which a relative distance and a relative speed ofa target are measured based on a beat signal generated from atransmission signal and a reception signal of a continuous wave radar,which is frequency modulated by a triangular wave, is characterized byincluding: frequency analysis means adapted to receive the beat signalin an up phase and in a down phase, respectively, for extractingfrequencies of the beat signal; frequency pair selection means forselecting a frequency pair corresponding to the target from thefrequencies of the beat signal in the up phase and in the down phaseextracted by the frequency analysis means; distance and speed derivingmeans adapted to receive the frequency pair selected by the frequencyselection means for obtaining the relative distance and the relativespeed of the target at present; distance and speed prediction meansadapted to receive the relative distance and the relative speed of thetarget at present from the distance and speed deriving means forcalculating an predicted distance value and an predicted speed value ofthe target after a lapse of a prescribed time while assuming themovement of the target; frequency prediction means adapted to receivethe predicted distance value and the predicted speed value from thedistance and speed prediction means for calculating an predictedfrequency value of the beat signal in the up phase or in the down phase;frequency comparison means for making a comparison between the predictedfrequency value of the beat signal predicted by the frequency predictionmeans and the frequency thereof after a lapse of the prescribed timethereby to determine the presence or absence of a beat frequency whosedifference in the above comparison result exists in the range of apreset allowable frequency width; and distance and speed smoothing meansfor calculating a smoothed distance value and a smoothed speed valuebased on the predicted distance value and the predicted speed value fromthe distance and speed prediction means, the predicted beat frequencyfrom the frequency prediction means, and an observed frequency value ofthe beat signal after a lapse of the prescribed time obtained by thefrequency analysis means; wherein relative distances and relative speedsof the target at the next and following observation times are obtainedby the distance and speed smoothing means through the use of only thebeat frequency in either one of the up phase and the down phase obtainedby the frequency prediction means.

[0031] Still further, the radar signal processing apparatus ischaracterized in that the frequency prediction means, the frequencycomparison means and the distance and speed smoothing means are providedin one set for each of the up phase and the down phase; at the next andfollowing measurement times, priority is given to the processing of thefrequency prediction means, the frequency comparison means and thedistance and speed smoothing means in either one of the up phase and thedown phase, and processing is carried out by the frequency predictionmeans, the frequency comparison means and the distance and speedsmoothing means in the other phase alone when no target is detected inthe one phase.

[0032] Besides, the distance and speed smoothing means is characterizedin that assuming that an predicted distance value, an predicted speedvalue, an predicted beat frequency value in the up phase, an predictedbeat frequency value in the down phase, an observed beat frequency valuein the up phase, and an observed beat frequency value in the down phase,at the next observation point in time t+Δt, are Rp(t+Δt), Vp(t+Δt),Up(t+Δt)x, Dp(t+Δt)x, U(t+Δt)x, and D(t+Δt)x, respectively, a smootheddistance value Rs(t+Δt) and a smoothed speed value Vs(t+Δt) arecalculated by using the following expression:

Rs(t+Δt)=Rp(t+Δt)+α×{Up(t+Δt)x−U(t+Δt)x}

Vs(t+Δt)=Vp(t+Δt)+β×{Up(t+Δt)x−U(t+Δt)x}

Rs(t+Δt)=Rp(t+Δt)+α×{Dp(t+Δt)x−D(t+Δt)x}

Vs(t+Δt)=Vp(t+Δt)+β×{Dp(t+Δt)x−D(t+Δt)x}

[0033] where α and β are constants.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a constructional view of a radar signal processingapparatus according to an embodiment of the present invention.

[0035]FIG. 2 is a flow chart illustrating a processing procedure formeasuring the relative distance and the relative speed of a target inthe radar signal processing apparatus of FIG. 1.

[0036]FIG. 3 is a view illustrating the frequency characteristics ofrespective signals relative to time in an FMCW radar.

[0037]FIG. 4 is a view illustrating the configuration of a signalprocessing part of a millimeter wave radar system disclosed in JapanesePatent Application Laid-Open No. 5-249233.

BEST MODE FOR CARRYING OUT THE INVENTION

[0038] Hereinafter, preferred embodiments of the present invention willbe described in detail while referring to the accompanying drawing.

[0039]FIG. 1 is a constructional view which shows a radar signalprocessing apparatus according to an embodiment of the presentinvention. In FIG. 1, the same parts as those of the known exampleillustrated in FIG. 4 are identified by the same symbols while omittingan explanation thereof. New symbols 101, 102 and 104 designate switchingparts, respectively. 103 designates a frequency pair selection part forselecting a frequency pair corresponding to a target from thefrequencies of a beat signal in an up phase and in a down phaseextracted by a frequency analysis part 12. 105 designates a distance andspeed prediction part which receives the current relative distance andrelative speed of the target from the distance and speed deriving part22 and calculates an predicted distance value and an predicted speedvalue after a lapse of a prescribed time while assuming or estimatingthe movement of the target.

[0040] Moreover, 106 and 107 designate frequency prediction parts whichreceive the predicted distance value and the predicted speed value fromthe distance and speed prediction part 105, and calculate predictedvalues of frequencies of the beat signal in the up phase and the downphase, respectively. 108 and 109 designate frequency comparison partswhich compare the predicted values of frequencies of the beat signalpredicted by the frequency prediction parts 106, 107 with thefrequencies of the beat signal after a lapse of a prescribed time,respectively, and determines the presence or absence of a beat frequencywhose difference in the comparison results exists in the range of apreset allowable frequency width. 110 and 111 designate distance andspeed smoothing parts which calculate smoothed values of the distanceand the speed based on the predicted values of the distance and thespeed from the distance and speed prediction parts 106, 107 and theobserved values of the frequencies of the beat signal from the frequencyprediction means.

[0041] In addition, FIG. 2 is a flow chart which shows a processingprocedure for measuring the relative distance and the relative speed ofa target in the radar signal processing apparatus shown in FIG. 1.

[0042] Now, reference will be made to the operation of the radar signalprocessing apparatus shown in FIG. 1 for measuring the relative distanceand the relative speed of the target in accordance with the procedure ofthe flow chart shown in FIG. 2.

[0043] The point in time at which a measurement operation is startedcorresponds to step P0, and the time t inside the signal processingapparatus is set to 0. At this time, the switching part 101 and theswitching part 102 are both connected to an A1 terminal, and theswitching part 104 is connected to a B0 terminal.

[0044] In step P1, the frequency analysis part 12 receives a beat signalin the up phase, which was converted into an digital signal by the A/Dconversion part 11, and extracts a frequency U(t)i of the beat signalthrough a frequency analysis using an FFT for instance. The frequencyU(t)i of the beat signal is input to the frequency pair selection part103 via the switching part 13 and the switching part 101.

[0045] In step P2, if it is determined as t=0 by referring to thepresent point in time t, the flow proceeds to step P3, whereas if it isdetermined as t≠0, the flow proceeds to step P9. Here, first assumingthat t=0, the flow proceeds to step P3.

[0046] In step P3, the frequency analysis part 12 receives a beat signalin the down phase, which was converted into a digital signal by the A/Dconversion part 11, and extracts a frequency D(t)j of the beat signalthrough a frequency analysis using an FFT for instance.

[0047] The frequency D(t)j of the beat signal is input to the frequencypair selection part 103 via the switching part 13 and the switching part101.

[0048] In step P4, if it is determined as t=0 by referring to thepresent point in time t, the flow proceeds to step P5, whereas if it isdetermined as t≠0, the flow proceeds to step P13. Here, first assumingthat t=0, the flow proceeds to step P5.

[0049] In step P5, the frequency pair selection part 103 selects afrequency pair {U(t)x, D(t)y} corresponding to a target from thefrequencies U(t)i and D(t)j of the input beat signal.

[0050] In step P6, the distance and speed deriving part 22 receives thefrequency pair {U(t)x, D(t)y}, and calculates, according to theexpressions (5) and (6) described above, a relative distance r(t) and arelative speed v(t) of the target at the present point in time, whichare output as measurement results through the switching part 104.

[0051] In step P7, the distance and speed prediction part 105 receivesthe relative distance r(t) and the relative speed v(t) of the target atthe present point in time, and calculates an predicted distance valueRp(t+Δt) and an predicted speed value Vp(t+Δt) in the next observationpoint in time t+Δt, while assuming or estimating the movement of thetarget. For instance, when it is assumed that the target performsuniform motion, the above calculations are carried out according to thefollowing expressions (11) and (12).

Rp(t+Δt)=r(t)+Δt×v(t)   (11)

Vp(t+Δt)=v(t)   (12)

[0052] In addition, the frequency prediction part 106 receives thepredicted distance value Rp(t+Δt) and the predicted speed valueVp(t+Δt), and calculates an predicted value Up(t+Δt)x of the frequencyof the beat signal in the up phase from the expression (1). Also, thefrequency prediction part 107 receives the predicted distance valueRp(t+Δt) and the predicted speed value Vp(t+Δt), and calculates anpredicted value Dp(t+Δt)x of the frequency of the beat signal in thedown phase from the expression (2).

[0053] In step P8, Δt is added to the time t inside the signalprocessing apparatus, a return is made to step P1 so as to perform themeasurement at time t+Δt.

[0054] In step P1, a beat frequency U(t+Δt)i is extracted in the samemanner as described above.

[0055] In step P2, assuming that t≠0, the flow proceeds to step P9.

[0056] In step P9, the frequency comparison part 108 makes adetermination as to the presence or absence of a beat frequency U(t+Δt)isatisfying the following expression (13) based on a preset allowablefrequency width Fu. That is, it is determined whether a target can bedetected in the up phase.

|Up(t+Δt)x−U(t+Δt)i|≦Fu   (13)

[0057] In step P10, if there is a beat frequency U(t+Δt)i satisfying theabove condition, it is set as U(t+Δt)x and the flow proceeds to stepP11, whereas if there is no such a beat frequency, the flow proceeds tostep P3. Here, first assuming that there is a U(t+Δt)x satisfying theabove condition, the flow proceeds to step P11.

[0058] In step P11, the distance and speed smoothing part 110 calculatesa smoothed distance value Rs(t+Δt) and a smoothed speed value Vs(t+Δt)from the predicted values Rp(t+Δt), Vp(t+Δt), Up(t+Δt)x and the observedvalue U(t+Δt)x according to the following expressions (14) and (15).

Rs(t+Δt)=Rp(t+Δt)+α×{Up(t+Δt)x−U(t+Δt)x}  (14)

Vs(t+Δt)=Vp(t+Δt)+β×{Up(t+Δt)x−U(t+Δt)x}  (15)

[0059] At this time, the switching part 104 is connected to a Buterminal, from which the smoothed distance value Rs(t+Δt) and thesmoothed speed values Vs(t+Δt) as calculated through the expressions(14) and (15) are output as the measurement results. That is, thedistance and the speed of the target are obtained only by the beatfrequency of the up phase.

[0060] In step P12, the distance and speed prediction part 105 receivesthe smoothed distance value Rs(t+Δt) and the smoothed speed valueVs(t+Δt) thus calculated by the expressions (14) and (15) as thedistance and the speed at present as in step P7, and calculates anpredicted distance value Rp(t+2Δt) and an predicted speed valueVp(t+2Δt) at the next observation point in time t+2Δt, while assumingthe movement of the target.

[0061] Further, the frequency prediction part 106 receives the predicteddistance value Rp(t+2Δt) and the predicted speed value Vp(t+2Δt), andcalculates an predicted value Up(t+2Δt)x of the beat frequency in the upphase from the expression (1). Also, the frequency prediction part 107receives the predicted values Rp(t+Δt) and Vp(t+Δt), and calculates anpredicted value Dp(t+2Δt)x of the beat frequency in the down phase fromthe expression (2).

[0062] In step P8, Δt is added to the time t inside the signalprocessing apparatus, and in order to perform the measurement at timepoint t+2Δt, a return to step P1 is performed and the above-mentionedoperations are carried out.

[0063] Next, reference will be made to the case where when there is noU(t+Δt)x in step P10, that is, when no target is detected, the flowproceeds to step P3. In step P3, D(t+Δt)j is extracted in the samemanner as described above.

[0064] In step P4, assuming that t≠0, the flow proceeds to step P13.

[0065] In step P13, the frequency comparison part 109 determines thepresence or absence of D(t+Δt)j satisfying the following expression (16)based on a preset allowable frequency width Fd.

|Dp(t+Δt)y−D(t+Δt)j|≦Fd   (16)

[0066] If there is no D(t+Δt)j in step P14, the flow proceeds to step P5and the above-mentioned operation is carried out.

[0067] On the other hand, if there is a D(t+Δt)j, it is set as D(t+Δt)yand the flow proceeds to step P15.

[0068] In step P15, the distance and speed smoothing part 111 calculatesa smoothed distance value Rs(t+Δt) and a smoothed speed value Vs(t+Δt)from the predicted values Rp(t+Δt), Vp(t+Δt) and Dp(t+Δt) y, and theobserved value D(t+Δt)y according to the following expressions, as instep P11.

Rs(t+Δt)=Rp(t+Δt)+α×{Dp(t+Δt)x−D(t+Δt)x}  (17)

Vs(t+Δt)=Vp(t+Δt)+β×{Dp(t+Δt)x−d(t+Δt)x}  (18)

[0069] At this time, the switching part 104 is connected to a Bdterminal, from which the smoothed distance value Rs(t+Δt) and thesmoothed speed values Vs(t+Δt) as calculated by the expressions (17) and(18) are output as measurement results. That is, the distance and thespeed of the target are obtained only by the beat frequency of the downphase.

[0070] In step P16, the distance and speed prediction part 105 receivesthe smoothed distance value Rs(t+Δt) and the smoothed speed valueVs(t+Δt) thus calculated by the expressions (17), (18) as the distanceand the speed at present, as in step P12, and calculates an predicteddistance value Rp(t+2Δt) and an predicted speed value Vp(t+2Δt) at thenext observation point in time t+2Δt, while assuming the movement of thetarget.

[0071] In addition, the frequency prediction part 106 receives Rp(t+2Δt)and Vp(t+2Δt), and calculates an predicted value Up(t+2Δt)x of the beatfrequency in the up phase from the expression (1). Also, the frequencyprediction part 107 receives Rp(t+Δt) and Vp(t+Δt), and calculates anpredicted value Dp(t+2Δt)x of the beat frequency in the down phase fromthe expression (2).

[0072] In step P8, Δt is added to the time t inside the signalprocessing apparatus, and in order to perform the measurement at timepoint t+2Δt, the flow returns to step P1, thus repeating theabove-mentioned operations.

[0073] Here, note that the individual components of FIG. 1 may beachieved by dedicated operational circuits, respectively. Alternatively,they may be implemented by a program built into a CPU (CentralProcessing Unit) or a DSP (Digital Signal Processor).

[0074] Moreover, in FIG. 2, the steps from P0 to P7 constitute a presentmeasurement stage, and the steps P8→P1→P2→P9→P12 constitute the next andfollowing measurement stages in which the relative distances and therelative speeds of the target at the next and following observationpoints in time can be measured by using only beat frequencies in the upphase. However, only beat frequencies in the down phase may be used inplace of those in the up phase. In the case of the measurement stagesconstructed such that measurements are carried out by using only beatfrequencies in the down phase, the steps P3→P4→P13-P16 may be replacedby a measurement stage where only beat frequencies in the up phase areused.

[0075] Thus, according to the above-mentioned embodiment, the relativedistance and the relative speed of a target can be obtained only byfrequencies in one phase, so it is possible to obtain measurementresults with high reliability by decreasing undetectable targets andfalse targets.

[0076] Moreover, one measurement processing according to frequencies inone phase alone is performed preferentially, and only when no target hasbeen detected by this measurement processing, another measurementprocessing according to frequencies in the other phase is then carriedout, whereby it is possible to obtain measurement results with highreliability by decreasing the number of undetectable targets.

[0077] Moreover, observed values, predicted values and smoothed valuesare used in the measurement processing according to frequencies in onephase alone, so that false targets can be reduced, thereby making itpossible to provide measurement results with high reliability.

[0078] In addition, the use of expressions (14), (15), (17) and (18) inthe measurement processing according to frequencies in one phase alonemakes it possible to provide accurate measurement results.

INDUSTRIAL APPLICABILITY

[0079] As described above, according to the present invention, byobtaining the relative distance and the relative speed of a target basedon the frequencies of a beat signal of up (or down) phase alone throughthe use of information in a time series direction of the frequencies ofthe beat signal of up (or down) phase, it is possible to provide adistance and speed measuring method and a radar signal processingapparatus using the method, which are capable of obtaining highlyreliable measurement results while reducing the number of false targetsand undetectable targets.

1. A distance and speed measuring method in which a relative distanceand a relative speed of a target are measured based on a beat signalgenerated from a transmission signal and a reception signal of acontinuous wave radar, which is frequency modulated by a triangularwave, said method being characterized by comprising: a presentmeasurement stage in which beat frequencies are extracted from the beatsignal in an up phase (modulation frequency increase period) and in adown phase (modulation frequency decrease period), and a frequency pairof beat frequencies corresponding to the target is selected among theextracted frequencies, the relative distance and the relative speed ofthe target being obtained based on the thus selected frequency pair asobserved values, from which a relative distance, a relative speed and abeat frequency of the target are obtained as predicted values at thenext observation time; and next and following measurement stages inwhich relative distances and relative speeds of the target at the nextand following observation times are measured by using only beatfrequencies in either one of the up phase and the down phase.
 2. Thedistance and speed measuring method according to claim 1, characterizedin that in said next and following measurement stages, priority is givento processing by beat frequencies in either one of the up phase and thedown phase, and processing by beat frequencies in the other phase aloneis carried out only when no target is detected in said one phase.
 3. Thedistance and speed measuring method according to claim 2, characterizedin that when relative distances and relative speeds of the target at thenext and following observation times are obtained by using only beatfrequencies in either one of the up phase and the down phase, said nextand following measurement stages use the observed values, the predictedvalues, and smoothed values which are obtained from the observed valuesand the predicted values.
 4. The distance and speed measuring methodaccording to claim 3, characterized in that assuming that an predicteddistance value, an predicted speed value, an predicted beat frequencyvalue in the up phase, an predicted beat frequency value in the downphase, an observed beat frequency value in the up phase, and an observedbeat frequency value in the down phase, at the next observation point intime t+Δt, are Rp(t+Δt), Vp(t+Δt), Up(t+Δt)x, Dp(t+Δt)x, U(t+Δt)x, andD(t+Δt)x, respectively, said next and following measurement stagescalculate a smoothed distance value Rs(t+Δt) and a smoothed speed valueVs(t+Δt) by using the following expression:Rs(t+Δt)=Rp(t+Δt)+α×{Up(t+Δt)x−U(t+Δt)x}Vs(t+Δt)=Vp(t+Δt)+β×{Up(t+Δt)x−U(t+Δt(x}Rs(t+Δt)=Rp(t+Δt)+α×{Dp(t+Δt)x−D(t+Δt)x}Vs(t+Δt)=Vp(t+Δt)+β×{Dp(t+Δt)x−D(t+Δt)x} where α and β are constants. 5.A radar signal processing apparatus in which a relative distance and arelative speed of a target are measured based on a beat signal generatedfrom a transmission signal and a reception signal of a continuous waveradar, which is frequency modulated by a triangular wave, said apparatusbeing characterized by comprising: frequency analysis means adapted toreceive the beat signal in an up phase and in a down phase,respectively, for extracting frequencies of the beat signal; frequencypair selection means for selecting a frequency pair corresponding to thetarget from the frequencies of the beat signal in the up phase and inthe down phase extracted by said frequency analysis means; distance andspeed deriving means adapted to receive the frequency pair selected bysaid frequency selection means for obtaining the relative distance andthe relative speed of the target at present; distance and speedprediction means adapted to receive the relative distance and therelative speed of the target at present from said distance and speedderiving means for calculating an predicted distance value and anpredicted speed value of the target after a lapse of a prescribed timewhile assuming the movement of the target; frequency prediction meansadapted to receive the predicted distance value and the predicted speedvalue from said distance and speed prediction means for calculating anpredicted frequency value of the beat signal in the up phase or in thedown phase; frequency comparison means for making a comparison betweenthe predicted frequency value of the beat signal predicted by saidfrequency prediction means and the frequency thereof after a lapse ofthe prescribed time thereby to determine the presence or absence of abeat frequency whose difference in the above comparison result exists inthe range of a preset allowable frequency width; and distance and speedsmoothing means for calculating a smoothed distance value and a smoothedspeed value based on the predicted distance value and the predictedspeed value from said distance and speed prediction means, the predictedbeat frequency from said frequency prediction means, and an observedfrequency value of the beat signal after a lapse of the prescribed timeobtained by said frequency analysis means; wherein relative distancesand relative speeds of the target at the next and following observationtimes are obtained by said distance and speed smoothing means throughthe use of only the beat frequency in either one of the up phase and thedown phase obtained by said frequency prediction means.
 6. The radarsignal processing apparatus according to claim 5, characterized in thatsaid frequency prediction means, said frequency comparison means andsaid distance and speed smoothing means are provided in one set for eachof the up phase and the down phase; at said next and followingmeasurement times, priority is given to the processing of said frequencyprediction means, said frequency comparison means and said distance andspeed smoothing means in either one of the up phase and the down phase,and processing is carried out by said frequency prediction means, saidfrequency comparison means and said distance and speed smoothing meansin the other phase alone when no target is detected in said one phase.7. The radar signal processing apparatus according to claim 5,characterized in that assuming that an predicted distance value, anpredicted speed value, an predicted beat frequency value in the upphase, an predicted beat frequency value in the down phase, an observedbeat frequency value in the up phase, and an observed beat frequencyvalue in the down phase, at the next observation point in time t+Δt, areRp(t+Δt), Vp(t+Δt), Up(t+Δt)x, Dp(t+Δt)x, U(t+Δt)x, and D(t+Δt)x,respectively, said distance and speed smoothing means (110, 111)calculates a smoothed distance value Rs(t+Δt) and a smoothed speed valueVs(t+Δt) by using the following expression:Rs(t+Δt)=Rp(t+Δt)+α×{Up(t+Δt)x−U(t+Δt)x}Vs(t+Δt)=Vp(t+Δt)+β×{Up(t+Δt)x−U(t+Δt)x}Rs(t+Δt)=Rp)t+Δt)+α×{Dp(t+Δt)x−D(t+Δt)x}Vs(t+Δt)=Vp(t+Δt)+β×{Dp(t+Δt)x−D(t+Δt)x} where α and β are constants.